CPII Drainage & Stormwater Management 1 — Questions and Answers
Question 1: What is the primary purpose of a stormwater detention basin in a public infrastructure project?
- To permanently store stormwater for irrigation use
- To temporarily hold stormwater runoff and release it at a controlled rate (Correct answer)
- To filter contaminants from stormwater before discharge
- To divert stormwater directly into the municipal sewer system
Correct answer: To temporarily hold stormwater runoff and release it at a controlled rate
Detention basins temporarily hold stormwater runoff and release it at a controlled rate to prevent downstream flooding.
Question 2: According to standard drainage design, what does the term 'return period' or 'recurrence interval' refer to?
- The time for stormwater to travel from the watershed to the outlet
- The frequency with which a given storm event is statistically expected to occur (Correct answer)
- The interval between scheduled maintenance of drainage structures
- The time required for a detention basin to empty after a storm
Correct answer: The frequency with which a given storm event is statistically expected to occur
Return period (recurrence interval) expresses the statistical probability that a storm of a given magnitude will occur in any given year.
Question 3: When inspecting a culvert, which condition is considered the most structurally critical defect?
- Surface rust on metal culverts
- Joint separation or cracking at the crown (Correct answer)
- Minor sediment accumulation at the inlet
- Faded paint or coating on the headwall
Correct answer: Joint separation or cracking at the crown
Joint separation or cracking at the crown indicates structural failure that can lead to collapse and loss of hydraulic capacity.
Question 4: What is the minimum slope typically recommended for concrete-lined drainage channels to maintain self-cleaning velocities?
- 0.1%
- 0.5% (Correct answer)
- 2.0%
- 5.0%
Correct answer: 0.5%
A minimum slope of 0.5% is typically required in concrete-lined channels to achieve the minimum velocity needed to prevent sediment deposition.
Question 5: Which federal regulation primarily governs stormwater discharges from construction sites disturbing one or more acres?
- Clean Air Act Section 112
- NPDES Construction General Permit under the Clean Water Act (Correct answer)
- Resource Conservation and Recovery Act (RCRA)
- Occupational Safety and Health Act (OSHA) 29 CFR 1926
Correct answer: NPDES Construction General Permit under the Clean Water Act
The NPDES Construction General Permit issued under the Clean Water Act requires stormwater pollution prevention plans for construction sites disturbing one or more acres.
Question 6: During a storm drain inspection, an inspector observes water pooling above a catch basin grate during moderate rainfall. What is the MOST likely cause?
- The upstream pipe slope is too steep
- The grate is undersized or clogged, restricting inlet capacity (Correct answer)
- The downstream pipe is oversized, causing backwater
- The headwall is improperly oriented
Correct answer: The grate is undersized or clogged, restricting inlet capacity
Ponding above a catch basin grate during moderate rain typically indicates the grate openings are clogged with debris or the grate is undersized for the drainage area.
Question 7: What is a Stormwater Pollution Prevention Plan (SWPPP) required to include as a primary component?
- A list of approved chemical treatments for runoff
- Best Management Practices (BMPs) to minimize pollutant discharge (Correct answer)
- A permit for discharging directly to navigable waters
- Certification from a licensed geotechnical engineer
Correct answer: Best Management Practices (BMPs) to minimize pollutant discharge
A SWPPP must identify and describe the Best Management Practices to be implemented to prevent pollutants from entering stormwater discharges.
CPII Drainage & Stormwater Management 1
What is the primary purpose of a stormwater detention basin in a public infrastructure project?